Process for the recovery of titanium dioxide and value metals and system for same

ABSTRACT

A process and system for recovering titanium dioxide and other value metals from a titanium bearing solid is disclosed. The process includes leaching the solid in hydrochloric acid to produce a leachate comprising undissolved solids and a leach solution comprising the titanium dioxide and the value metals, wherein the hydrochloric acid concentration is maintained above a value required to maintain the titanium dioxide and the value metals dissolved in the leach solution at atmospheric pressure. The leachate is separated into the leach solution and the undissolved solids. The concentration of hydrochloric acid concentration in the leach solution is reduced to recover titanium dioxide by hydrolysis and precipitation to produce a titanium dioxide rich slurry. In a preferred embodiment, HCl is recovered with a matrix solution.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of PCT/CA2011/000142 filed Feb. 4, 2011, currently pending, which, in turn, claims the benefit of U.S. provisional Application No. 61/301,458 filed Feb. 4, 2010, U.S. provisional Application No. 61,305,718 filed Feb. 18, 2010 and U.S. provisional Application No. 61/420,500 filed Dec. 7, 2010, the disclosures of which are incorporated in their entirety by reference herein.

TECHNICAL FIELD

The present invention relates to a process and system for recovery of titanium dioxide and value metals from ores, intermediates or concentrates.

BACKGROUND

A process for the extraction of iron from iron-containing titaniferous ores is described in U.S. Pat. No. 2,167,628 and U.S. Pat. No. 2,406,577 of Alessandroni et al., who disclose the leaching of titaniferous ore with a solution of hydrochloric acid of a specific gravity of approximately 1.10 and at least 0.5 mole of a soluble chloride e.g. alkali metal chlorides, alkaline earth metal chlorides and aluminum chloride, at a temperature between 70° C. and the boiling point of the solution. The specific gravity of 1.10 is stated to correspond to a concentration of hydrochloric acid of about 230 g/L i.e. about 21% hydrochloric acid. The selective extraction of iron is illustrated. In the former U.S. Pat. No. 2,167,628, it is described as being necessary to reduce any iron present to the ferrous state in order to recover substantially pure titanium dioxide by hydrolysis.

Similarly, Zirngibl et al. in U.S. Pat. No. 3,236,596 describe a method for decomposing titanium minerals in order to recover titanium dioxide. This process also requires that any ferric iron be first reduced to ferrous in order to recover a pure form of titanium dioxide by hydrolysis.

In U.S. Pat. No. 4,058,393, McLaughlin describes a method of dissolving titanium minerals wherein it is necessary to add a fluoride to the mixture. The purpose of the fluoride is to break down the silicate matrix of the titanium mineral, thereby allowing the titanium to be dissolved. Subsequent hydrolysis of the solution, however, yields a mixed titanium dioxide-fluoride compound. As with the above processes, it is necessary to reduce ferric iron to ferrous to prevent iron contamination of the subsequent titanium precipitate.

In U.S. Pat. No. 3,202,524, Thomson describes a process for the recovery of a pure form of titanium dioxide. In this process, it is first necessary to calcine the titanium-bearing feedstock in order to both destroy the mineral structure, and also to render any iron present in a form which will not dissolve. Subsequent leaching of the calcined mineral requires the addition of either lime or magnesia to further ensure that there is no residual iron in solution prior to hydrolysis to recover titanium dioxide. The method is specific to the titanium minerals rutile or leucoxene, neither of which has any substantial iron component.

A process for leaching ilmenite is described in U.S. Pat. No. 3,903,239 of S. A. Berkovich. The process comprising contacting ilmenite, or a concentrate thereof, with concentrated hydrochloric acid lixiviant solution at a temperature of about 15-30° C. to solubilize and leach from the ore at least 80% and preferably at least 95% of the iron and titanium values. The leaching time is typically 3-25 days, using counter-current flow or the use of closed cycle loops in which hydrochloric acid is continuously passed through a bed of the ore. The reaction is exothermic, and cooling of the reactants may be required. Subsequent to leaching, ferric ion in the lixiviant solution is converted to ferrous ion e.g. using a gaseous reductant such as sulphur dioxide, after which the solution is subjected to hydrolysis. The ore may be pre-treated prior to contact with the concentrated hydrochloric acid to increase the rate of dissolution of titanium and iron values during leaching. The pre-treatment is a smelting step that may include oxidation at elevated temperature e.g. 600-1000° C. in the presence of air or oxygen, followed by a reduction of at least part of the iron oxide in the ore with carbon or carbon monoxide.

One other known process described by Verhulst et al., at the 32nd Annual Hydrometallurgy Meeting, METSOC, Chloride Metallurgy 2002, Vol. II, pg 417-432, uses concentrated hydrochloric acid to dissolve both the iron and titanium components of ilmenite, named the Altair process, and was developed by Altair Nanomaterials Inc., (Reno, Nev.). In this process, ilmenite is dissolved with recycled concentrated HCl. Iron powder is used to reduce Fe(III) to Fe(II), followed by a bulk removal of iron from solution by crystallization of FeCl2 and also eliminates any ferric iron, which would compromise the subsequent solvent extraction step. This then permits the selective removal of titanium using solvent extraction (SX1). The Ti-rich solution from SX1 will undergo a second solvent extraction step, where residual iron is recovered, leaving a concentrated solution of titanium chloride, which is then spray hydrolyzed under controlled conditions to make TiO2 hydrate. This material is said to be a pigment grade product.

U.S. Pat. No. 6,375,923 of Duyvesteyn et al. and “The Altair TiO2 Pigment Process and its Extension into the Field of Nanomaterials” by D. Verhulst, B Sabacky, T. Spitler and W. Duyvesteyn, pages 417-432, Chloride Metallurgy 2002 Volume II, 32nd Annual Hydrometallurgy Meeting, Edited by E. Peek and G. Van Weert, published by CIM, describe a hydrometallurgical process for producing pigment-grade titanium dioxide from a titaniferous ore. The process comprises leaching the ore with a solution of hydrochloric acid at a temperature of at least 50° C. to provide a leachate of titanium chloride, ferrous chloride, ferric chloride and impurity chlorides, a residue of undissolved solids and sufficient excess hydrochloric acid to prevent precipitation of titanium dioxide. The lixiviant used has a high chloride content, especially >400 g/L, and the vapour pressure of the solution is greater than atmospheric. The leachate is separated from solids and the ferric ions in the leachate are reduced to ferrous ions. The solution is then cooled to crystallize ferrous chloride. The resultant solution containing titanium ions, ferric ions and ferrous ions is contacted with a water-immiscible organophosphorus extractant. The pregnant strip solution containing titanium and ferric ions, and a minor amount of ferrous ions, is contacted with an amine extractant. The raffinate obtained, which contains titanium ions, is hydrolyzed to produce titanium dioxide. HCl solutions from pyrohydrolysis and from TiO2 hydrolysis are combined and converted into HCl gas and water by pressure-swing distillation, which is a very expensive process and energy-consuming process.

U.S. Pat. No. 6,500,396 of V. I. Lakshmanan et al. describes a method for the production of titanium metal from titanium-bearing ore. In one embodiment, ore or concentrate is leached with an aqueous solution of a hydrogen halide, especially hydrochloric acid, at a temperature of at least 90° C., followed by a solids/liquids separation and extraction with an immiscible organic phase. In other embodiments, the ore is leached with the hydrogen halide in the presence of an oxidizing agent. A variety of oxidizing agents are disclosed, including air, hydrogen or other peroxides, or sodium or other perchlorates. In the leach solution, iron is solubilized and titanium is converted into titanium dioxide.

U.S. Pat. No. 7,803,336 by V. I. Lakshmanan et al., describes a method for the production of titanium metal from titanium-bearing ore. The method provides a process for leaching a value metal from a titanium-bearing ore material containing said value metal, said titanium-bearing ore material being selected from the group consisting of a titanium-bearing ore, concentrate thereof, intermediates and tailings thereof, and mixtures thereof, comprising the step of leaching the titanium-bearing ore material at atmospheric pressure with a lixiviant comprising hydrochloric acid at a concentration of less than 20% (mass ratio), and a chloride selected from the group consisting of alkali metal chlorides, magnesium chloride and calcium chloride, and mixtures thereof.

The previously described hydrometallurgical processes involve digestion of the ore in a mineral acid, such as hydrochloric acid or sulphuric acid, to extract at least the titanium values from the ore, but generally the iron and vanadium values are also extracted. Each process requires a purification process step of the leach solution before TiO2 recovery is achieved, either the reduction of any ferric iron to its ferrous state, or a separate solvent extraction step to recover the titanium in a pure form.

In the light of the above, an alternative process that provides cost-efficient extraction of titanium dioxide and vanadium from titanium-bearing ores or concentrates is required that achieves this cost advantage by recovering TiO₂ and vanadium directly from the non-purified leach solution.

SUMMARY

It is therefore an aim of the present invention to provide a process for the recovery of pigment grade (being defined as titanium dioxide of purity ≧98.5% TiO₂) titanium dioxide and value metals from titanium bearing materials from a non-purified leach solution containing TiO₂, as well as, other metals dissolved by hydrochloric acid.

Therefore, in accordance with the present invention, there is provided a process for recovery of pigment grade titanium dioxide and value metals from a titanium bearing solid, the process comprising the steps of: (a) leaching the solid in hydrochloric acid to produce a leachate comprising undissolved solids and a leach solution comprising the titanium dioxide and the value metals, wherein the hydrochloric acid concentration is maintained above a value required to maintain the titanium dioxide and the value metals dissolved in the leach solution at atmospheric pressure; (b) separating the leachate into the leach solution and the undissolved solids; and (c) reducing the concentration of hydrochloric acid concentration in the leach solution to recover titanium dioxide by hydrolysis and precipitation to produce a titanium dioxide rich slurry.

In accordance with one aspect of the present invention, there is provided the process described herein, wherein reducing the hydrochloric acid concentration is by heating the leach solution and removing free HCl by HCl distillation of the leach solution.

In accordance with yet another aspect of the present invention, there is provided the process described herein, wherein the titanium dioxide slurry is separated in a solid/liquid separator and the TiO₂-free filtrate produced in the separator is further treated to recover vanadium.

In accordance with still another aspect of the present invention, there is provided the process described herein, wherein the further treatment of the TiO₂-free filtrate is by solvent extraction with an extractant and the further treatment produces a vanadium free raffinate.

In accordance with yet still another aspect of the present invention, there is provided the process described herein, wherein the extractant is D2EHPA (di-2-ethyl hexyl phosphoric acid) or LIX63.

In accordance with another aspect of the present invention, there is provided the process described herein, wherein the extractant is LIX63.

In accordance with yet still another aspect of the present invention, there is provided the process described herein, further comprising mixing the raffinate with a matrix solution to produce a reaction mixture and adding an oxygen containing gas to the oxygenate the mixture with HCl production.

Further in accordance with the present invention, there is provided a system for recovering titanium dioxide comprising: a) a leaching section comprising a vessel comprising an ore inlet for a titanium dioxide bearing solid, an acid inlet for hydrochloric acid, an agitator mixing the titanium dioxide bearing solid and the acid to produce a leachate comprising a leach solution and undissolved solids; and a leachate outlet for discharging the leachate; b) a solid liquid separator comprising a leachate inlet hydraulically connected to the leachate outlet, a separation device hydraulically connected to the leachate inlet, for separating the leach solution from the undissolved solids, the device comprising an undissolved solids discharge and a leach solution outlet; and c) a titanium dioxide precipitator for reducing the concentration of the acid in the leach solution and recovering titanium dioxide by precipitation from the leach solution, the precipitator comprising a leach solution inlet hydraulically connected to the leach solution outlet, an HCl acid outlet, and titanium dioxide slurry outlet.

In accordance with one embodiment of the present invention, there is provided the system described herein, wherein the titanium dioxide precipitator comprises a heater for boiling the leach solution to liberate free HCl via the HCl acid outlet and a means of collecting and discharging the precipitated a titanium dioxide slurry.

In accordance with another embodiment of the present invention, there is provided the system described herein, further comprising an acid condenser hydraulically connected to the HCl acid outlet condensing the free HCl.

In accordance with yet another embodiment of the present invention, there is provided the system described herein, further comprising means of recycling the condensed free HCl to the leaching solution.

In accordance with still another embodiment of the present invention, there is provided the system described herein, further comprising a solvent extraction system hydraulically linked to the leach solution outlet, the solvent extraction system for extractant LIX63 comprising a raffinate outlet.

In accordance with yet still another embodiment of the present invention, there is provided the system described herein, wherein the raffinate outlet is hydraulically linked to a HCl recovery system comprising a circulating matrix solution and an injection inlet for an oxygen containing gas.

In accordance with a further embodiment of the present invention, there is provided the system described herein, wherein the HCl recovery system comprising a reactor for recovering hydrochloric acid and for oxidation/hydrolysis of metal from metal chloride solution, the reactor comprising: a tank compatible with a mixture comprising the metal chloride solution, a matrix solution, an oxygen containing gas and a solid comprising a metal oxide, the tank comprising a base, the base defining a first diameter and a first cross sectional area, the base comprising a metal oxide slurry outlet, a matrix solution outlet and a gas inlet; a top opposite the base, the top comprising a solution inlet, a hydrochloric acid outlet, a matrix solution inlet, the top defining gas an expansion zone having a second cross sectional area and, a wall attached to the top and the base defining a volume and a height of the tank; wherein a ratio of the second cross sectional area to the first cross sectional area is greater than 1 and whereby the hydrochloric acid leaves the mixture as a hydrochloric acid containing gas in the gas expansion zone at the top of the tank.

In accordance with yet a further embodiment of the present invention, there is provided the system described herein, wherein the reactor comprises an aspect ratio of the height to the first diameter from 5 to 1-20 to 1.

In accordance with still a further embodiment of the present invention, there is provided the system described herein, wherein the circulating matrix solution comprises ZnCl₂.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawing, showing by way of illustration a particular embodiment of the present invention and in which:

FIG. 1 is a block diagram of a process for the recovery of titanium dioxide and value metals from titanium-bearing ore or concentrate according to one embodiment of the present invention.

DETAILED DESCRIPTION

The present invention relates to a process for leaching of a value metal from a titanium-bearing material. In particularly preferred embodiments, the present invention is directed to the recovery of titanium in the form of pigment-grade quality titanium dioxide from titanium-bearing ores, especially ilmenite or titaniferous magnetite. In particular, the present invention relates to processes operated at atmospheric pressure for leaching titanium-bearing ores containing value metals, especially at least one of titanium, vanadium or iron. Titanium is the preferred value metal but where present in sufficient quantities, vanadium is also recovered. The value metal content of the ore may vary widely in type and amount, depending on the source of the ore.

Referring now to FIG. 1, the process 1 is operated at atmospheric pressure, using recycled hydrochloric acid 13 that is about 10% to 35% (mass %). Such a concentration of acid may be obtained by hydrolytic distillation of chloride solutions.

The titanium-bearing feed material 5 is preferably an ore, but may be a concentrate or intermediate. FIG. 1 uses the abbreviation RoM (run of mill) ore.

Referring to FIG. 1, ore 5 in a form as discussed above is fed to a chloride leach step 10 in which the ore 5 is contacted and leached with a lixiviant comprising a chloride and hydrochloric acid 13, optionally also containing an oxidant 12. The concentration of hydrochloric acid is 10% (mass ratio) to 35%. Sufficient excess acid is added to ensure that premature precipitation of titanium dioxide does not occur. It is also important to keep the temperature below 70° C., and preferably in the range 50-60° C.

The chloride leach step 10 may be conducted continuously as a co-current step, a countercurrent step or in another manner, or the leaching step may be conducted as a batch step. The leaching step 10 is carried out at atmospheric (ambient) pressure i.e. it is not necessary to conduct the leaching step under pressure. In preferred embodiments, the leaching step 10 is carried out with hydrochloric acid having a maximum concentration of 30-35% (mass %).

The leaching section of the present system that encompasses block 1 of FIG. 1 includes a vessel that is adapted for HCl acid and suspended solids. The vessel has at least: a solids inlet for a titanium dioxide bearing solid; an acid inlet for hydrochloric acid; an agitator mixing the titanium dioxide bearing solid and the acid and a leachate outlet for discharging the value-metal rich leachate 19. The agitation of the raw material entering the vessel produces the leachate that is a suspension of the leach solution and undissolved solids.

The value metal-rich slurry (leachate) 19 is produced in the leach step is typically in the form of a suspension. The leachate 19 is fed to a solid/liquid separation step 20 to effect separation of leachate 19 into a leach solution 29 and a solids fraction 25 e.g. leach residue and other gangue. Techniques for such separation are known and are performed by solid/liquid separators such as a pressure or vacuum filter, counter-current decanter or centrifuge. In a preferred embodiment the solid/liquid separator is a vacuum belt filter.

In order to recover value metals, the leachate 29 obtained from the above solids/liquid separation step is subjected to one or more steps to separate value metals. Techniques for the separation and recovery of value metals from the leachate will be apparent to persons skilled in the art. For instance, value metals especially titanium in the form of the metal per se or as titanium dioxide, may be recovered from the leach solution by standard or other known methods. For example, separation methods e.g. ion exchange, solvent extraction or precipitation, may be used to remove impurities e.g. iron, chromium and vanadium, followed by recovery of titanium as, in particular titanium metal or especially titanium dioxide, using e.g. precipitation. Some of these techniques are discussed in the aforementioned U.S. Pat. No. 6,500,396. One example of a separation procedure is illustrated in FIG. 1, and steps shown are discussed herein.

However, an important advantage of the present process is that the production of pigment-quality TiO₂ can be undertaken directly from the leach solution 29, after solids removal without any further recovery process steps. The titanium values in the leach solution 29 will be in the form of a titanium chloride compound. In a preferred embodiment, the leach solution 29 is heated to its boiling point in a TiO₂ recovery step 30 to distill off any free hydrochloric acid 33, as a gas which is condensed and collected for recycle for to chloride leach 10. The action of eliminating the acid causes titanium dioxide to be formed by hydrolysis and precipitates. Therefore, the titanium dioxide is recovered in a TiO₂ precipitator that is understood to be included within the block 30 of FIG. 1. The precipitator is adapted to allow a reduction of the concentration of the HCl in the leach solution 29 and the precipitation of the TiO₂ solid and removal thereof in a TiO₂ slurry 39. The precipitator has at least: a leach solution inlet, an HCl acid outlet and a titanium dioxide slurry outlet.

In another embodiment, water may also be added to assist in the hydrolysis step in TiO₂ recovery 30, but water (not shown) is an optional addition. In another optional embodiment, ferric iron in the leach solution 29 is first reduced to ferrous iron by the addition of metallic iron powder, prior to heating and titanium dioxide hydrolysis; represented by the following reactions:

TiCl₄+2H₂O═TiO₂+4-HCl;

TiOCl₂+H₂O═TiO₂+2HCl.

The TiO₂ slurry 39 is fed to a solid liquid separation step where the TiO₂ 45 is removed for example by vacuum filtration, and a TiO₂ free filtrate 49 is produced.

The titanium dioxide-free filtrate 49 may be treated to recover vanadium 50. In one embodiment, when the solution is predominantly ferrous iron chloride, vanadium may be recovered by ion exchange or by solvent extraction with the extractant D2EHPA (di-2-ethyl hexyl phosphoric acid). When the solution is predominantly ferric iron chloride, the solvent extractant LIX 63 is preferred, thereby removing vanadium 55. The vanadium 55 may be recovered in any one of several forms including vanadium pentoxide, VOCl₃, VCl₃ and combinations thereof, where vanadium pentoxide is preferred The loaded resin and D2EHPA solvent extractant is stripped with hydrochloric acid or the solvent extractant, The LIX63 is scrubbed with water and stripped with caustic soda and ammonia is added to produce in situ ammonium chloride which precipitates ammonium metavanadate which may then be calcined to produce vanadium pentoxide or vanadium trioxide depending on the temperature of the furnace, the furnace atmosphere and appropriate residence time.

Subsequent to the removal of vanadium, the resultant ferrous or ferric or mixtures thereof chloride solution 59 is heated to approximately 180° C. in a Fe₂O₃ recovery step 60, where oxidation and hydrolysis takes place, recovering iron as a solid iron oxide 75, that is substantially hematite in a solid/liquid separation step 70. Simultaneously, high strength HCl 63 is recovered for recycle. Substantially hematite is defined, as mainly hematite with less that 7% by weight of other materials.

The process for recovering hydrochloric acid and generating iron oxide is similar to U.S. Pat. No. 3,682,592 issued to Kovacs, which describes a process, the PORI Process, for recovering HCl gas and ferric oxide from waste hydrochloric acid steel mill pickle liquors, and also a more recent patent application describing the SMS Siemag process, which has been published by N. Takahashi et al., entitled Processing Method for Recovering Iron Oxide and Hydrochloric Acid, International Patent Application WO2009153321A1, Dec. 23, 2009.

Therefore, the method of the present invention combines the iron precipitation/hydrochloric acid recovery process with titanium dioxide precipitation. In a preferred embodiment this iron recovery 70 and precipitation can occur after TiO₂ recovery. The iron recovery 70 is by Fe₂O₃ precipitation and Fe₂O₃ recovery 75. Similarly, a barren Fe free MgCl₂ containing solution 79 which is left over can be treated in a MgO recovery step 80 by the reactions including:

MgCl₂+H₂O═MgO+2HCl

The leaching process 10 may be conducted continuously in at least one stirred tank reactor. Preferably, at least two reactors are used.

In the alternative for HCl recovery and Fe₂O₃ precipitation, a matrix solution may be used in the present process, and may be any compound which is capable of being oxygenated to form, even transiently, a hypochlorite compound, and which remains liquid at temperatures up to at least 190° C., and preferably up to 250° C. It is also preferable that said matrix solution will act as a solvent for any base and light metals which might be present in the feed ferrous iron solution. In practice, there are very few such materials. Zinc chloride is a preferred matrix. Other such compounds are calcium chloride and magnesium chloride, and it is understood that there may be other such matrices alone or in combination. In this application, particularly where the feed is ferrous chloride solution 59, zinc chloride is preferred since it is both a chloride salt and remains liquid to a temperature >250° C.

The matrix solution remains fluid at such temperatures, and the hematite solids are removed by any suitable separation device, for example hot vacuum or pressure filtration.

The matrix solution is substantially inert, but acts as a catalyst for oxygen transfer to accelerate the oxidation and hydrolysis reactions. The matrix solution is generally a molten salt hydrate, e.g. ZnCl₂.2H₂O in a liquid state and in various states of hydration ZnCl₂.2H₂O to ZnCl₂.5H₂O depending on the temperature.

The definition of a base metal is understood as a non-ferrous metal but excluding the precious metals (Au, Ag, Pt, Pd, etc.).

The HCl recovery/Fe₂O₃ precipitation method is conducted in an inert matrix solution according to one embodiment of the present invention, the method steps comprising: an iron oxidation from the solution 59 including light metals (in this case Mg), iron recovery hydrolysis 70 with HCl removal and recycle 63 and hematite production, solid/liquid separation 70 of the hematite 75, a hydrolysis of the light metals 80 with a further HCl recovery and recycle 83 and MgO separation 26, and recycle of the inert matrix solution 74.

The ferrous chloride solution 59 is added and mixed into the matrix solution together with air or oxygen 61 at 130-160° C. to produce a reaction mixture. Any ferrous iron may be oxidized and subsequently hydrolysed by water at 170-180° C. to form hematite according to the following chemical reactions with HCl 63 produced:

12FeCl₂+30₂→2Fe₂O₃+8FeCl₃   I

4FeCl₂+O₂+4H₂O→2Fe₂O₃+8HCl   II

2FeCl₃+3H₂O→Fe₂O₃+6HCl   III

Therefore, the reaction mixture 69 includes: the liquor solution, the matrix solution, the precipitating metal solids, any dissolved solids, unreacted oxygen and HCl. While air can be used to effect the oxidation, its use is not recommended, unless sub-azeotropic (<20% HCl) hydrochloric acid is acceptable to the overall process. This is because the large quantity of nitrogen present in air requires the addition of water to scrub the hydrochloric acid liberated into the off-gas system.

Following the hydrolysis/precipitation 60 step, the remaining solution 69/reaction mixture (now an iron-depleted matrix chloride liquor) including the hematite product 75 are then subjected to a solid/liquid separation step 70. The hematite product thus recovered may be dried and sold, or simply disposed of.

Once the iron has been removed 75, most of the magnesium-rich matrix solution 74 is simply recycled in order to build up the concentration of Mg.

The remaining matrix solution 79 will contain magnesium chloride.

Heating the solution 79 to 220-225° C. will effect the precipitation 50 of magnesium, according to the following reaction using water and/or steam and with HCl 83 produced:

MgCl₂+H₂O→Mg(OH)Cl+HCl   VI

The magnesium compounds 89 may be separated from solution leaving hydrolysis by any appropriate separation device, washed and dried.

The matrix reactor in a preferred embodiment is a column reactor, defined as tank with a height that is greater than its diameter by at least 5 times. A column reactor is distinguished from a stirred tank reactor, in that it does not have mechanical agitation. In a particularly preferred embodiment, the column reactor the liquid flow through the column reactor is downward and countercurrent to the oxygen containing gas flow upward through the column reactor. Advantages of such a column reactor include a preliminary separation of hematite solid in the direction liquid flow downward towards a solids separation apparatus. In a stirred tank reactor the solids would remain equally suspended. However, the process could be performed at lower efficiency in a stirred tank reactor as will be seen in the Examples.

Broadly speaking, the process involves the oxidation and hydrolysis of ferrous iron of the ferrous chloride solution with recovery of associated hydrochloric acid and an iron material (hematite). In one embodiment, the reactor comprises electrical heating coils, which are used to heat the reactor to maintain the desired temperature of operation. The heating coils can alternatively be replaced with a jacketed reactor with a thermal fluid such a steam as the heating medium.

In one embodiment of the present invention, ferrous iron is oxidized to ferric, hydrolysing the ferric iron and recovering hydrochloric acid and useful metal oxidic materials from any chloride-based feed solution.

In accordance with another aspect of HCl/iron precipitation, there is provided a method of recovering hydrochloric acid and metal from a ferrous chloride liquor wherein the improvement comprises injecting the liquor into an oxygenated matrix solution in a reaction column countercurrent to the gas flow, wherein the solution assists hydrolysis of the metal and HCl production.

The matrix column reactor has an oxygen containing gas injected at the bottom and the ferrous iron chloride, removed from the base. The weight of the liquid in the column, of height 1-2 meters, and preferably 1.4-1.8 meters, holds up the oxygen gas in the column, thereby providing sufficient time for the reactions to take place. There may be a plurality of such reactors, maintained at a temperature of 109-250° C. In a specific embodiment of the invention, the first reactor is preferably at 130-170° C., and more preferably at 140-160° C.

The temperature of additional reactors in series may be raised to 170-250° C., and more preferably to 180-200° C., in order for the hematite particles to grow. It has been discovered that by maintaining temperature gradients, different particle sizes of hematite in the range 1-100 microns may be formed, thus generating hematite particles with differing color and size. Finer particles will be red in colour, whereas larger, more dense particles vary in color from purple to black.

The reactor, in a preferred embodiment, has an aspect ratio of reactor height to diameter (in the base portion) of from 5 to 1 to 20 to 1.

The top portion of the reactor may comprise a further sampling or injection, as well as a gas expansion zone. The top portion further includes a ferrous chloride solution feed inlet, a hydrochloric acid collection outlet and an optional gas outlet, if a second reactor is connected in series.

The uppermost sampling and injection port typically includes an inlet for the circulation of the matrix solution.

The matrix solution is usually withdrawn from the bottom-most sampling and injection unit via outlet. From outlet the matrix solution including a slurry of produced hematite is pumped to a solid removal step, such as filtration.

The present reactor is meant to oxygenate the matrix solution that generates a concentration, however transient, of hypochlorite, according to the following reaction (using zinc as an example):

ZnCl₂+O₂→Zn(OCl)₂   (1)

This reaction is favoured in the temperature range 140-160° C., and if there is relatively little associated free water present. Free water is water which is purely a solvent and is not bound in any way to the ions of the matrix compound. As described earlier, the zinc chloride is present as a molten salt hydrate, thus satisfying these requirements.

The ferrous chloride solution may be added from the top of the reactor, such that it meets the oxygenated matrix solution countercurrently. The hypochlorite solution is a very powerful oxidant and thus highly reactive, and instantaneously reacts with the ferrous iron according to the following reaction:

Zn(OCl)₂+4FeCl₂+4HCl→4FeCl₃+ZnCl₂+2H₂O   (2)

The HCl for reaction (2) is provided by reaction (III) previously presented:

2FeCl₃+3H₂O→Fe₂O₃+6HCl   (III)

The overall effect is thus as shown in reaction (II) previously presented:

4FeCl₂+O₂+4H₂O→2Fe₂O₃+8HCl (II)

Additional water for the reaction is provided by that associated with the incoming feed solution. The concentration of the incoming feed solution may be adjusted to give the desired strength showing ports for the addition of fresh ferrous iron feed, a port for the collection of hydrochloric acid vapour, and a third port for unused oxygen gas to proceed to the next reactor.

While air can be used to effect the oxidation, its use is not recommended, unless sub-azeotropic (<20% HCl) hydrochloric acid is acceptable to the overall process. This is because the large quantity of nitrogen present in air requires the addition of water to scrub the hydrochloric acid liberated into the off-gas system.

Therefore, the process of recovery of TiO₂ of the present invention does not require pre-treatment of the titanium-bearing ore prior to the leaching step.

A particular advantage of the process 1 of the present invention is that high rates of extraction of value metals are obtained in a leaching step that operates at atmospheric pressure with hydrochloric acid. It is not necessary to operate the leaching step under pressure. The use of atmospheric pressure results in substantial economic advantages, especially in capital costs. Value metals may be recovered. The use of chloride chemistry offers advantages in operating and capital costs of the process. Leaching agent may be regenerated and recycled, especially using hydrolysis step. The use of hydrochloric acid permits recovery and recycle of hydrochloric acid (33, 63, 83) to the leaching step 10, especially with relatively small amounts of make-up hydrochloric acid.

Therefore the method of the present invention is conducted in a system having at least three principal components. The first component is a leaching section where the hydrochloric acid leach 10 is performed. The leaching section comprises a vessel having a solids inlet for the titanium dioxide bearing solid, an acid inlet for hydrochloric acid required to leach the titanium dioxide bearing solid, an agitator that is used to mix the solid and acid. Within the vessel, a leachate is produced and comprises a leach solution containing dissolved titanium and value metals as well as undissolved solids in suspension. The leaching section vessel also comprises an outlet for discharging the leachate.

The second component of the system is a solid/liquid separator connected hydraulically to the leaching section. The separator includes a leachate inlet connected to the leachate outlet of the leaching section. The separator further has a separation device hydraulically connected to the leachate inlet that separates the leach solution from the undissolved solids. The device comprises an undissolved solids discharge and a leach solution outlet. In a preferred embodiment, the solid/liquid separator is a vacuum belt filter.

The third component of the system is a titanium dioxide precipitator where the concentration of the hydrochloric acid in the leach solution is reduced. With the reduction of concentration of hydrochloric acid the titanium dissolved in solution is hydrolyzed and precipitates from the leach solution. The precipitator includes a leach solution inlet hydraulically linked to the leach solution outlet of the solid liquid separator, an HCl acid inlet and a titanium dioxide slurry outlet.

In a preferred embodiment, the titanium dioxide precipitator comprises a heater either within the precipitator or in an external circulating loop that heats the leach solution to boiling, thus liberating free HCl as gas via the acid outlet. This free HCl gas can then be condensed via a condenser and preferably recycled back to the leaching section.

The present invention is illustrated by the following examples.

EXAMPLE 1

100 g ore, crushed to 325 mesh, was leached in 850 mL of solution at 95° C. for four hours. Sufficient HCl (as 35% solution) was added to account for 120% of the total Fe, V, Ti, Mn and Mg. Ore analysed 50.8% Fe, 16.0% Ti and 0.27% V.

Results:

TABLE 1 Metal Extraction, % Time, hours Fe Ti V 0 43.3 25.6 n/a 1 94.0 72.0 n/a 2 94.1 23.1 n/a 3 92.2 13.7 n/a 4 92.3 5.3 99.9

The results in Table 1 show the chloride leach essentially complete in 1 hour. The Ti dissolves and then hydrolyses (re-precipitates) as TiO₂ as the free HCl is depleted. Therefore, during leaching, it is important to maintain enough free acid to keep the Ti in solution, so that the unleached solids can be filtered off.

EXAMPLE 2

A series of tests was carried out with Fe/Ti/V solution from the leached ore. The free HCl was distilled off and the Ti then hydrolyzed to form TiO₂ solids. As the hydrolysis reaction proceeds, more HCl is produced, and this was constantly distilled off. Average HCl concentration in the distillate was 100 g/L HCl (10% HCl). Analysis of the TiO₂ solids recovered is found in Table 2:

TABLE 2 % Ti % Fe 54.2 3.04 57.6 2.17 57.7 2.09

No V was detected. Al was 0.45% and Mg 0.1%.

Pure TiO₂ is 59.8% Ti, hence these solids are good quality. Recovery of Ti from the leach solution averaged 99.7%.

EXAMPLE 2

A continuous miniplant was operated for 10 days leaching a titaniferous magnetite ore containing 20% TiO₂, 0.38% V₂O₅ and 67% Fe₃O₄. Residence time was 20 minutes and temperature was maintained at 50° C. Ti and V extractions averaged close to 95% at steady state, and iron extraction was 80%.

The resulting leach solution, on average analyzing 18.5 g/L Ti, 700 mg/L V and 100 g/L Fe, of which 70% was in the ferric form, was subjected to Ti hydrolysis by raising the temperature to 95° C. Ti recovery was 99.9%, with an average analysis of 99% TiO₂, which is the equivalent of pigment grade titanium dioxide.

This example demonstrates that under the conditions of this patent application, pigment-grade TiO₂ can be produced directly from solutions containing high concentrations of ferric iron.

EXAMPLE 3

Spent leach solution from titanium hydrolysis, analysing 2.1 g/L V, was adjusted with hydrogen peroxide to 835 mV ORP, and was then contacted with 40% LIX63 in ISOPAR-M at an A/O ratio of 2:1 for ten minutes at 45° C. 93.5% of the V and <1% of the iron was extracted into the organic phase. The organic was then stripped with 1M NaOH (1M NH₄OH could equally have been used) under the same conditions, resulting in 100% of the V reporting to the aqueous phase. Ammonium chloride (NH₄Cl) was then added to the strip solution to precipitate ammonium metavanadate, which analysed 43.66% V (theoretical analysis is 43.54% V). This example demonstrates the effectiveness of solvent extraction in recovering at high efficiency and highly pure vanadium from the leach liquor.

EXAMPLE 4

A series of tests was carried out on the titanium-free solution to recover iron oxide. The results were as shown below:

TABLE 3 Characteristics of Iron Oxide Solids Produced in Example 4 Residue Test No. Colour % Fe % hum H9 Purple 71.0 13.5 H10 Black 69.3 H11 Red 60.0 H14 Black 66.7 10 H19C Black 65.2 8 H20C Beige 63.0 13

The embodiments of the invention described above are intended to be exemplary. Those skilled in the art will therefore appreciate that the foregoing description is illustrative only, and that various alternate configurations and modifications can be devised without departing from the spirit of the present invention. Accordingly, the present invention is intended to embrace all such alternate configurations, modifications and variances which fall within the scope of the appended claims. 

What is claimed is:
 1. A process for recovery of titanium dioxide and value metals from a titanium bearing solid, the process comprising the steps of: (a) leaching the solid in hydrochloric acid to produce a leachate comprising undissolved solids and a leach solution comprising the titanium dioxide and the value metals, wherein the hydrochloric acid concentration is maintained above a value required to maintain the titanium dioxide and the value metals dissolved in the leach solution at atmospheric pressure; (b) separating the leachate into the leach solution and the undissolved solids; and (c) reducing the concentration of hydrochloric acid concentration in the leach solution to recover titanium dioxide by hydrolysis and precipitation to produce a titanium dioxide rich slurry.
 2. The process of claim 1, wherein reducing the hydrochloric acid concentration is by heating the leach solution and removing free HCl by HCl distillation of the leach solution.
 3. The process of claim 1, wherein reducing the hydrochloric acid concentration is by adding water to the leach solution.
 4. The process of claim 1 wherein pigment grade TiO₂ is recovered directly from solutions containing ferric iron.
 5. The process of claim 1, wherein the titanium dioxide slurry is separated in a solid/liquid separator and the TiO2 free filtrate produced in the separator is further treated to recover vanadium.
 6. The process of claim 5, wherein the further treatment of the TiO₂ free filtrate is by solvent extraction with an extractant and the further treatment produces a vanadium free raffinate.
 7. The process of claim 6, wherein the extractant is D2EHPA (di-2-ethyl hexyl phosphoric acid) or LIX63.
 8. The process of claim 6, wherein the extractant is LIX63.
 9. The process of claim 6, further comprising mixing the raffinate with a matrix solution to produce a reaction mixture and adding an oxygen containing gas to the oxygenate the mixture with HCl production.
 10. The process of claim 7, wherein the matrix solution comprises ZnCl₂.
 11. A system for recovering titanium dioxide comprising: a) a leaching section comprising a vessel having an ore inlet for a titanium dioxide bearing solid, and an acid inlet for hydrochloric acid, an agitator mixing the titanium dioxide bearing solid and the acid to produce a leachate comprising a leach solution and undissolved solids; and a leachate outlet for discharging the leachate; b) a solid liquid separator comprising a leachate inlet hydraulically connected to the leachate outlet, a separation device hydraulically connected to the leachate inlet, for separating the leach solution from the undissolved solids, the device comprising an undissolved solids discharge and a leach solution outlet; and c) a titanium dioxide precipitator for reducing the concentration of the acid in the leach solution and recovering titanium dioxide by precipitation from the leach solution, the precipitator comprising a leach solution inlet hydraulically connected to the leach solution outlet, an HCl acid outlet, and titanium dioxide slurry outlet.
 12. The system according to claim 11, wherein the titanium dioxide precipitator comprises a heater for boiling the leach solution to liberate free HCl via the HCl acid outlet and a means of collecting and discharging the precipitated a titanium dioxide slurry.
 13. The system of claim 11, further comprising an acid condenser hydraulically connected to the HCl acid outlet condensing the free HCl.
 14. The system of claim 11, further comprising means of recycling the condensed free HCl to the leaching solution.
 15. The system of claim 11, further comprising a solvent extraction system for extractant LIX63 hydraulically linked to the leach solution outlet, the solvent extraction system comprising a raffinate outlet.
 16. The system of claim 15, wherein the raffinate outlet is hydraulically linked to a HCl recovery system comprising a circulating matrix solution and an injection inlet for an oxygen containing gas.
 17. The system of claim 16, wherein the HCl recovery system comprising a reactor for recovering hydrochloric acid and for oxidation/hydrolysis of metal from metal chloride solution, the reactor comprising: a tank compatible with a mixture comprising the metal chloride solution, a matrix solution, an oxygen containing gas and a solid comprising a metal oxide, the tank comprising a base, the base defining a first diameter and a first cross sectional area, the base comprising a metal oxide slurry outlet, a matrix solution outlet and a gas inlet; a top opposite the base, the top comprising a solution inlet, a hydrochloric acid outlet, a matrix solution inlet, the top defining gas an expansion zone having a second cross sectional area and, a wall attached to the top and the base defining a volume and a height of the tank; wherein a ratio of the second cross sectional area to the first cross sectional area is greater than 1 and whereby the hydrochloric acid leaves the mixture as a hydrochloric acid containing gas in the gas expansion zone at the top of the tank.
 18. The system of claim 16, wherein the reactor comprises an aspect ratio of the height to the first diameter from 5 to 1-20 to
 1. 19. The system of claim 16, wherein the circulating matrix solution comprises ZnCl₂. 